For automatic or semi-automatic transmissions the gear shift operation during engine operation is performed based on an assessed available engine torque. For certain vehicles, e.g. heavy vehicles such as trucks, the gear shift may according to a variant be effected through shifts of one or more steps, e.g. a one-step shift, a two-step shift, a three-step shift, etc. depending on the available engine torque.
The gear shift operation comprises an off-ramp phase in which the torque is reduced to substantially zero. Then there is a synchronization phase in which the gear shift is completed by disengaging the current gear and engaging the chosen gear. During the synchronization phase the engine is synchronized to the next target speed. After the synchronization phase the gearbox controller returns the torque control to the driver demanded torque. The driver demand torque is supplied to the engine, increasing the available torque up to a level where an exhaust gas smoke limiting function of the combustion engine limits the development of available engine torque up to a driver demand torque. During a gear shift operation engine operation parameter values including boost pressure are affected which in turn have influence on emissions, engine efficiency and driveability.
In order to assess the gear shift operation, tests are made with the specific vehicle in order to determine the available engine torque. This however does not provide an accurate assessment in that the engine torque may vary due to the boost pressure to such an extent that the chosen gear is not the most suitable gear.
There is thus a need for improving engine operation control in connection to a gear shift operation.